Industrial adhesive bonding, especially in the wood, bookbinding and packaging sectors, is carried out by means of machines operating at a high output rate, the setting time of the bonding being generally less than a few seconds.
To reach this output rate, it is known to employ hot-melt adhesives which have the property of bonding various materials merely by cooling. These adhesives consist chiefly of a polymer which gives the adhesive its mechanical properties, a tackifying resin with high adhesiveness when hot and, where appropriate, a rheology-modifier such as an oil, a wax, or a plasticizer.
The hot-melt adhesives of the prior art are generally based on a polymer chosen from copolymers of ethylene and of vinyl acetate (EVA), polyamides, poly-alpha-olefins essentially amorphous ("amorphous poly-alpha-olefins" or APAO) and mixtures of APAO and of a copolymer of ethylene and of vinyl acetate or of alkyl (meth)acrylate (see FR-A-2 721 039 and AU-B-63181/90).
However, the adhesives just mentioned exhibit disadvantages in the course of the adhesive bonding in the abovementioned conditions.
Thus, EVA-based adhesives have a limited temperature strength. For example, in the wood sector the strength is of the order of 80 to 110.degree. C. depending on the nature of the edge employed.
Adhesives containing a polyamide are stable only at a temperature lower than 200.degree. C. and are liable to be degraded by oxidation. In addition, they are high in cost.
Adhesives including an APAO have a slow increase in cohesion, which makes it necessary to lengthen the period of holding the articles under pressure and hence to reduce the output rate. In addition, the bonding frequently includes, downstream of the machine, a stage of in-line cutting of the articles by means of guillotines and/or saws the blades of which are rapidly fouled by incompletely hardened adhesive. Furthermore, these adhesives form threads on coating devices, for example using a roll or intermittent nozzle, and this produces, on the one hand, fouling of the machine and, on the other hand, soiling on the bonded articles.